1. Field of the Invention
The present invention relates to a multi-stage pulley having a plurality of groove portions around which driving belts can be wound and to a method for producing the same.
2. Description of the Related Art
In a known method for producing a multi-stage pulley, disclosed in, for example, Kokai (Jpn. Unexamined Patent Publication) No. 63-63544, groove portions are formed by a plastic deformation of a workpiece(a blank for a multi-stage pulley), using a groove forming roller which is provided with a plurality of groove forming portions, integral therewith, which are coaxially arranged.
Since each groove portion is formed by a plastic deformation of the blank for a multi-stage pulley using the groove forming roller, the groove forming roller is subjected to a shearing stress at its front end due to the plastic deformation. Thus, in the known apparatus described in the above-mentioned publication, there is a high probability that the groove forming roller is damaged during the formation of the grooves.
Furthermore, in the known apparatus described in the above-mentioned publication, if only one of the groove forming portions is damaged, the entirety of the groove forming roller must be replaced, because the groove forming portions are formed integratedly. Therefore, the known apparatus described in the above-mentioned publication has a problem in that as the cost of the groove forming roller increases, the manufacturing cost of the multi-stage pulley increases.
In consideration of the above-mentioned problem, an object of the present invention is to reduce the manufacturing cost of a multi-stage pulley by preventing the groove forming roller from being damaged.
The present invention, in order to achieve the above-mentioned objects, uses the following technical means.
In a first invention, a plurality of groove portions (101) are formed on an outer peripheral wall (103) of a pulley body (102) generally in the form of a cup and a damping portion (104) having a smaller rigidity than the groove portions (101) is formed between the groove portions (101).
With this structure, an effect that the stress produced due to the plastic deformation upon forming the groove portions (101) is absorbed by the damping portion (104) if the groove portions (101) are formed while the damping portion (104) is pressed, can be obtained.
Note that the damping portion (104) is preferably made of an annular groove recessed toward the inner side of the pulley body (102).
According to a second invention, the production method is characterized by comprising an annular groove forming step, in which an annular groove (104) recessed toward the inner side of a workpiece (W2) generally in the form of a cup is formed between the portions of the outer peripheral wall of the workpiece W2 corresponding to the groove portions (101), and a groove forming step, in which the groove portions (101) are formed on the outer peripheral wall of the workpiece (W2), with the annular groove (104) being pressed.
With this structure, firstly, the annular groove (104) functions as a damping portion having a smaller rigidity than the groove portions (101) and hence, the stress produced due to the plastic deformation during the formation of the groove portions (101) can be absorbed by the annular groove (104).
Therefore, no excessive shearing stress acts on the front ends of the groove forming rollers (206 and 207) in the groove forming process, and thus, not only can the groove forming rollers (206 and 207) be prevented from being damaged, but also no unwanted plastic deformation of the groove portions (101) takes place, leading to an increased dimensional accuracy of the multi-stage pulley (100).
Secondly, since the groove portions (101) are formed while pressing the annular groove (104), it can be ensured in the present invention that no unwanted plastic deformation of the groove portions (101) occurs.
As stated above, according to the present invention, is since the yield of the multi-stage pulley can be improved without increasing the equipment investment for the groove forming rollers (206 and 207), the manufacturing cost of the multi-stage pulley (100) can be reduced.
The annular groove (104) is preferably pressed by the annular groove forming roller (204) which is adapted to form the annular groove (104).